Traditional wireless networks include a number of base stations (BTS) and one or more mobile switching centers (MSC)/base station controllers (BSC). The BTSs each cover a geographic region, or cell of the wireless network and communicate with mobile telephones in the cell. The MSCs/BSCs provide switch and soft handoff functionality for the wireless network. To support data calls, wireless networks typically include a data interworking function (IWF). The IWF connects the wireless network to the Internet or other data network.
Each cell of a wireless network is able to support a certain number of wireless calls. This capacity is a function of frequency reuse, carrier to interference ratio, bit-energy to noise ratio, effective bit-rate protocol and other criteria of the wireless link. The wireless link may be based on established standards such as IS-54 (TDMA), IS-95 (CDMA), GMS and AMPS, 802.11 based WLAN, new upcoming standards such as CDMA 2000 and W-CDMA or proprietary radio protocols.
For CDMA and other radio-link protocols, Internet protocol (IP) and other packets are fragmented into a number of radio frames that are transmitted over the wireless link. In the event of transmission errors, a frame is retransmitted up to a set number of times. If the frame is not successfully received by such retransmissions, the radio-link protocol aborts delivery of the frame, continues with the succeeding frames and leaves it to packet layer protocols to recover the lost data. The allowed number of retransmissions is set by negotiation during initiation of a connection.